In population PK, how can maturation of renal function be incorporated?

• A. Use a maturation function to adjust renal clearance with age.
• B. Rely only on weight, not maturation.
• C. Ignore maturation in renal clearance.
• D. Rely only on hepatic function.

Answer: (A)

Maturation of renal function is captured by adding a maturation function that modulates renal clearance as a function of age (often via postnatal or postmenstrual age). In population PK, you describe renal clearance as a product of an allometric weight term and a maturation factor: CLrenal(age) = CLrenal_adult × Maturation(age) × (Weight/Weight_std)^0.75. The maturation factor is typically a sigmoidal (Hill-type) function that starts near zero at birth and rises toward one as the child ages, with parameters like PMA50 (the age at 50% maturation) and the Hill coefficient controlling the steepness. This approach reflects that kidney function develops over time and affects drug elimination, beyond what weight alone can explain.

So using a maturation function to adjust renal clearance with age best represents how renal elimination matures from infancy to adulthood, whereas relying on weight alone, ignoring maturation, or focusing only on hepatic function would miss these developmental changes in renal clearance.